1. Field of the Invention
This invention relates generally to a method and apparatus for establishing a servicing mode of an electronic apparatus, and more particularly is directed to such method and apparatus suitable for use in connection with a color television receiver of the inner bus-type in which the signal processing circuits are controlled by means of a microcomputer or central processing unit (CPU).
2. Description of the Prior Art
Video and audio apparatus using digital signal processing circuits, such as, television receivers, video tape recorders (VTRs) and audio tape recorders have become commercially available. Most such digital video and audio apparatus use inner or internal bus lines for interconnecting a microcomputer or CPU, a memory, and other control circuitry. In a normal operating mode of the video and audio apparatus, the CPU fetches data corresponding to standardized control signal values for the several signal processing circuits of the apparatus and which have been previously stored in the memory. The CPU sends the fetched data to the appropriate circuit by way of the internal bus lines so as to suitably control the operation of the respective signal processing circuit. Further, the CPU may control the signal processing circuits of the apparatus in response to signals supplied thereto by manual actuation of a keyboard or a remote commander or controller, thereby permitting the changing, at will, of the conditions of the signal processing circuits. The provision of a television receiver with an internal or inner bus system has the advantage of permitting standardized, centralized and simplified testing of the circuitry of the receiver during assembling and servicing thereof, thereby substantially reducing the manufacturing and maintenance cost. A television receiver provided with such an internal bus system is disclosed, by way of example, in U.S. Pat. No. 4,701,870, which has a common assignee herewith.
In the case of an inner bus television receiver, the data stored in the memory in correspondence to predetermined conditions of the adjustable circuits, for example, for establishing standardized values of contrast, hue and balance of a displayed color image, may be rewritten or changed to data corresponding to other values or predetermined conditions when testing the operation of the television receiver at the time of its manufacture, or when the television receiver is undergoing maintenance or servicing and it is found necessary to adjust such characteristics of the displayed image due to secular changes that have occurred in components of the receiver. In order to rewrite or change the data stored in the memory, it is necessary to establish a servicing mode of the television receiver. For this purpose, known television receivers of the inner bus type have been provided with a change-over switch which is manually actuable for changing from the ordinary operation mode to the servicing mode of the television receiver. However, when such manually actuable change-over switch is provided, there is the danger that a user of the television receiver may inadvertently actuate such switch and thereby establish the servicing mode of the television receiver, in which mode, the stored data for establishing the standardized conditions of the displayed color image may be disturbed.
In order to avoid the foregoing problem, an inner bus television receiver may be arranged so that, when electric power is supplied to the receiver, establishment of the servicing mode thereof requires that a plurality of switches, such as, the switches associated with the channel selection keys or push-buttons, need to be actuated in a predetermined order. Although the foregoing arrangement reduces the chances of inadvertently establishing the servicing mode of the television receiver, it is nevertheless still possible that the keys or push-buttons may, by chance, be actuated in the predetermined order for establishing the servicing mode and thereby permitting disturbance of the data stored in the memory for maintaining the standardized conditions of the displayed image.